Purpose: The CatalystTM system was tested and compared with an X-ray image verification system for patient positioning during breast cancer treatment. Included was to find the optimal reference image and the optimal cropping method for the reference image. Parameters that could lead to an optimization of the treatment routines were also evaluated.

Method and Material: The study was divided into three parts, “Accuracy measurement of the scanning volume”, “The Catalyst system correspondence with CBCT verification images on a phantom” and “The Catalyst system correspondence with planar verification images on patients.”

Accuracy measurements of the scanning volume were performed with a head shaped phantom which had skin equivalent... (More)

Purpose: The CatalystTM system was tested and compared with an X-ray image verification system for patient positioning during breast cancer treatment. Included was to find the optimal reference image and the optimal cropping method for the reference image. Parameters that could lead to an optimization of the treatment routines were also evaluated.

Method and Material: The study was divided into three parts, “Accuracy measurement of the scanning volume”, “The Catalyst system correspondence with CBCT verification images on a phantom” and “The Catalyst system correspondence with planar verification images on patients.”

Accuracy measurements of the scanning volume were performed with a head shaped phantom which had skin equivalent characteristics. The phantom was positioned in a coordinate table and was moved in steps of 2 millimeters in lateral and longitudinal direction in four different planes to investigate the accuracy in the scanning volume.

The CBCT study was performed with a pelvis phantom. The phantom was moved ten times and the deviation from the reference images in the CBCT system and the CatalystTM system were compared.

Results: The results of the study “Accuracy measurement of the scanning volume” showed that the system has a limit at 7.5 cm above the isocenter and that the most accurate results were registered in the plane 5.0 centimeters above the isocenter. The error in the positioning result was 0-4.0 millimeters in the scanning volume. There was no detectable drift in the values in lateral, longitudinal or vertical direction.
The CatalystTM system correspondence with CBCT verification images on a phantom resulted in a high accuracy in positioning in vertical and lateral direction with a correspondence of 0-2.0 millimeters. In the longitudinal direction the results differed between 4.0-6.0 millimeter and which was probably due to a flat structure of the phantom.
The results from the patient positioning study varied depending on the patient. The optimal reference image was determined to be from the CT structure set. An optimal cropping method for the reference image was found and later used for the analysis of the patient positioning.

Conclusions: The CatalystTM system shows accurate positioning result for the phantom studies. The limitation was due to flat or spherical surfaces where the algorithm had difficulties. The flat structure did not provide enough matching information for the algorithm and for the spherical shape the optimization method found a number of solutions. This implies that it is important that the reference image in a patient situation has some structure that the system can use for matching.
In the patient positioning study the reference image for every patient were cropped in an optimal way, mainly to minimize the breathing motion. The results of the study indicated that the system does not correspond well with the planar verification images enough for all patients, possible due to that the verification image system matches due to bony structure and the Catalyst system matches due to the skin surface. (Less)